Sunday, March 03, 2013

Midweek Storm Snows On DC, Perhaps Not Here?

Last night's computer models continue to agree that the midweek storm tracks south of us, but close enough to bring some accumulating snow to Washington DC and a lot of accumulating snow to the mountains of Virginia and West Virginia.

We likely will be on the northern fringe of this storm system, dependent on the influence of a strong (for March) ridge of high pressure that's in place across Eastern Canada in the mid atmosphere. You can see this ridge laid out on the graphic below as the low pressure center moves to our south, intensifying as it does so. The influence of this mid level high is strong enough to prevent the surface low from moving too far to the north once the low reaches the coast and intensifies. However, we're close enough to the low that some precipitation will fall in parts of the area.

The best chance for notable precipitation will be farther to our south...those details are still fluid in terms of specific precipitation layout and where heavier precipitation falls. Snow is possible in heavier swaths of precipitation and those could set themselves up across Southern Delaware and Maryland, with rain and snow mixed farther to the north up to perhaps Dover, Millville, even Wilmington. Barring a rather marked north shift, there's probably not a lot of precipitation that falls north of the Pennsylvania Turnpike -- there could be a few sleet pellets, snowflakes, or sprinkles across the far northern burbs. Light rain, perhaps mixed with snow, could fall across the Philly metro, but it's just as likely that nothing more than sprinkles and flurries falls unless there's a nudge to the north with the track of this storm system. Both the Euro and GFS generally agree on the same general concept of southern areas getting some precipitation, with northern areas missing out on much of anything.

Shore areas probably have issues with beach erosion and coastal flooding to deal with from this storm on Wednesday and Thursday. Sustained winds to 40 mph are looking more likely at the Shore, gusts could exceed 50 mph with this storm. The pressure gradient between the surface low across the Tidewater and high pressure over Quebec will provide a channel for strong east and northeasterly winds. The worst impacts from a beach erosion and coastal flooding standpoint probably set up below Atlantic City and include the Delaware Beaches, particularly Lewes. Modeling on storm surge and tidal flooding suggests the possibility of near record tidal flooding at Lewes on Thursday AM at high tide. The storm itself won't be terribly strong from a pressure standpoint but contrasting with a strong high to the north is allowing for winds to be gusty and coastal impacts to increase.

Again, any north shift nudges impacts north. However, given the relative consistency in the Euro the past couple of days and the GFS lining up for three consecutive runs (through the early AM run) in near lockstep with the Euro, it seems like we have a relatively decent handle on track and detail for Wednesday and Wednesday night's storm -- and that the bulk of activity from this storm from a precipitation standpoint likely sets up to our south.